1. Technical Field of the Invention
The present invention generally relates to a variable displacement compressor having a swash-ring construction. More specifically, the present invention relates to a variable displacement swash-ring compressor having a stepped shaft.
2. Description of the Prior Art
In an automotive vehicle equipped with air conditioning, a compressor is used to pump coolant through the air conditioning system to cool the vehicle. Most often, the compressor is driven by a serpentine belt of the vehicle and, hence, the speed of the compressor is controlled by the speed of the vehicle. In order to provide consistent operation of the air conditioning system, variable displacement compressors have been developed to allow the compressor to provide constant performance at all vehicle speeds. In a variable displacement compressor, higher displacement is necessary when the vehicle is idling or running at low speeds. When the vehicle is running at high speeds, the compressor is cycling much more rapidly, and therefore can provide equivalent performance at a lower displacement.
The typical automotive air conditioning compressor uses multiple pistons to pump the coolant through the system. The pistons are driven back and forth within the compressor by a plate or ring that is attached to a rotating shaft. The plate or ring is mounted at an angle relative to the shaft and engages each of the pistons. Due to the angle of the ring, radial positions around a periphery of the ring have varying axial positions within the compressor. The pistons are fixed radially within the compressor housing, so that as the shaft and ring rotate the pistons slide along the periphery of the ring and are thereby moved axially back and forth with rotations of the shaft and ring. Variable displacement is achieved by limiting the stroke of the pistons. Variable displacement compressors are available in three basic types: 1) wobble plate compressors, 2) swash-plate compressors, or 3) swash-ring compressors. The present invention is related to a swash-ring compressor.
In a swash-ring compressor, the pistons within the compressor are driven by a swash-ring. Variable displacement, by limiting the stoke of the pistons, is achieved by varying the angle of the swash-ring relative to the rotating shaft. U.S. Pat. No. 6,164,252 describes the construction of a variable displacement swash-ring compressor and is hereby incorporated by reference into the present application.
In the ""252 patent, a sleeve is slidably mounted for limited axial movement along the compressor""s shaft and a swash-ring is pivotally mounted onto the sleeve. A pin, rigidly mounted within and extending from the shaft, engages the swash-ring at an axial distance from the pivotal connection between the swash-ring and the sleeve. As the sleeve slides along the shaft, the swash-ring moves axially with the sleeve at the pivotal connection, but cannot move axially at the point where the pin engages the swash-ring. This causes the swash-ring to pivot about the point where the pin engages the swash-ring, thereby changing the angle of the swash-ring relative to the shaft.
As a result of the pin transferring rotation to the swash-ring, the pin undergoes very high stresses that require the diameter of the shaft to be large enough to provide sufficient strength to support the pin. Specifically, the shaft is provided with a constant diameter over the entire length along which the sleeve slides. This makes the shaft very heavy and forces other components within the compressor to be designed around the large diameter of the shaft.
As seen from the above, there is a need to improve the design of a shaft for a compressor so that the compressor can be made lighter and more compact.
It is therefore an object of the present invention to provide an improved variable displacement compressor of lighter weight and more compact construction.
A further object of the present invention is to provide a variable displacement compressor having a stepped shaft which will reduce the size and weight of the shaft, as well as allowing other compressor components to be designed smaller and lighter.
The disadvantages of the prior art are overcome by providing a variable displacement swash-ring compressor with a stepped shaft. Use of the stepped shaft reduces the size and weight of the shaft, and therefore the compressor itself, as well as allowing other compressor components to be designed smaller and lighter.
In one aspect, the present invention is a compressor that includes a shaft rotatably mounted within the compressor. A sleeve is slidably supported on the shaft and includes collar portions, at opposite ends thereof, that support the sleeve on the shaft. A swash-ring is pivotally mounted onto the sleeve such that the swash-ring is angularly adjustable with respect to the shaft. A pin is fixedly mounted to and extends from the shaft and a distal end of the pin pivotally engages the swash-ring. The connection between the swash-ring and the pin forces the swash-ring to rotate with the shaft, while allowing the swash-ring to be angularly adjusted relative to the shaft.
The shaft includes a step adjacent the pin, defining a reduced diameter portion on the shaft and end thereof. By way of this step and reduced diameter portion, an annular gap is formed between the shaft and the inner diameter of the sleeve where the sleeve overlies the reduced diameter portion of the shaft. The annular gap therefore extends along a portion of the sleeve between the first and second collar portions. The sleeve is further biased along the shaft by a spring whose position may be varied.
In another aspect of the present invention, the shaft includes a pair of steps, with each of the steps being located on opposing sides of the pin.
Further variations on the invention include various locations for the spring and for a positive stop for the sleeve. The positive stop can be defined by the step within the shaft, or, the shaft may include a snap ring groove with a snap ring engaged therein to define a positive stop for the sleeve.